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Factors controlling biomass distributions in marine benthic organisms (meio- to macrofauna, 1 µg-32mg wet weight) were investigated through observations and allometric modelling. Biomass (and abundance) size spectra were measured at three locations: the Faroe-Shetland Channel in the north-east Atlantic (FSC, water depth 1600 m, September 2000); the Fladen Ground in the North Sea (FG, 150 m, September 2000); and the hypoxic Oman Margin (OM, 500 m, September 2002) in the Arabian Sea. Biomass increased with body size through a power law at FG (allometric exponent, b = 0.16) and at FSC (b = 0.32), but less convincingly at OM (b was not significantly different from -1/4 or 0). Our results question the assumption that metazoan biomass spectra are bimodal in marine sediments. The model incorporated 16 metazoan size classes, as derived from the observed spectra, all reliant on a common detrital food pool. All physiological (ingestion, mortality, assimilation and respiration) parameters scaled to body size following optimisation to the data at each site, the resulting values being consistent within expectations from the literature. For all sites, body size related changes in mortality played the greatest role in determining the trend of the biomass size spectra. The body size trend in the respiration rate was most sensitive to allometry in both mortality and ingestion, and the trend in body size spectra of the production: biomass ratio was explained by the allometry in ingestion. Our results suggest that size-scaling mortality and ingestion are important factors determining the distribution of biomass across the meiofauna to macrofauna size range in marine sedimentary communities, in agreement with the general observation that biomass tends to accumulates in larger rather than smaller size classes in these environments. [ABSTRACT FROM AUTHOR]

DYMONIS is a numerical model designed to test the interaction of processes linking increased inputs of nutrients to possible increases in phytoplankton production (eutrophication). Originally developed for the North Sea, it has been applied to the Irish Sea. A basic process, which must be modelled before more complex ones, is represented by the salinity field, which passively traces the mixing of river and sea water. To fit the observed data, this requires a 1.5-fold increase in the current estimate of rain inputs. This is reasonable, given the uncertainty in estimates of such inputs. Comparison with model output of observed salinities from the long-term data series from the Isle of Man “Cypris” station shows that real weather effects on circulation have a greater effect on salinity than probable changes in river discharges. Nutrient concentrations are determined by the mixing of river and ocean waters, removal by autotrophic organisms and return from detrital phases. The model shows that the minimum nitrate concentration in winter in the southern Irish Sea is a consequence of the varying balance of these processes with time. It can be demonstrated that long-term increases in the concentration of nitrate off the Isle of Man could be a simple artefact of the increase in river and atmospheric inputs and of the essentially estuarine nature of the Irish Sea. [ABSTRACT FROM PUBLISHER]